The present invention relates generally to a process for producing organic halide compounds, and more in particular to a process for producing substituted benzotrihalide compounds.
Substituted benzotrihalide compounds are a known class of compounds used in various commercial applications. One of the most valuable applications is as an intermediate in making herbicides such as, for example, trifluralin, benefin, fluchlovalin, dinitramine, profluralin, ethyl fluralin, chloramber, 2,3,6-trichlorobenzoic acid, and the like.
Various methods have been employed to produce substituted benzotrihalides. In one method, 4-chlorobenzotrichloride was produced by a multi-step reaction starting with toluene. In this reaction, toluene was chlorinated in the presence of iron chloride at a temperature of from about 90.degree. to about 100.degree. C. to form an isomeric mixture of ortho- and para- chlorotoluene which was resolved by distillation. The para-isomer was then reacted with gaseous chlorine in the presence of ultraviolet light to chlorinate the side chain carbon of the chlorotoluene molecule. The resulting 4-chlorobenzotrichloride has been converted to 4-chlorobenzotrifluoride by methods such as that taught in U.S. Pat. No. 4,045,502.
In another method for producing 4-chlorobenzotrichloride, toluene was sulfonated with chlorosulfonic acid to form a mixture of the ortho- and para- isomers of toluenesulphonyl chloride. This isomeric mixture was resolved on the basis of melting points. The para-isomer was then converted to 4-chlorobenzotrichloride by allowing it to react with chlorine in an inert medium under irradiation with ultraviolet light as described in U.S. Pat. No. 3,230,268 and by B. Miller, and C. Walling in J. Am. Chem. Soc., 79, 4187 (1957).
Nearly all the present industrial processes for producing the substituted benzotrihalides, especially the monosubstituted benzotrihalides, suffer from the disadvantage of producing a mixture of position isomers which must be resolved.
A need, therefore, exists for a process which produces good yields of the desired product while selectively controlling the production of position isomers, especially the ortho- and para-isomers of the monosubstituted compounds.